Understanding the role of catalysts in the leaching of sulfide minerals

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Chalcopyrite is the world's most abundant copper mineral, accounting for roughly 70% of the world's total copper production. Most chalcopyrite concentrates are processed by smelting. However, smelters release sulfur dioxide gas (the leading cause of acid rain), cannot handle impurities such as arsenic (a common element in many copper orebodies), and are typically very remote from copper minesites (incurring high shipping charges and contributing to greenhouse gas emissions). Leaching presents a promising alternative to smelting. Leaching emits no gases, can handle arsenic in an environmentally sensitive manner, can be applied to low grade materials, and can be operated directly at minesites. However, chalcopyrite is among the most difficult of all sulfide minerals to leach, as it tends to form passive layers under typical oxidative leaching conditions. Many processes have been developed over the years to overcome this passivity, relying on a combination of ultrafine grinding, highly corrosive chemical additives (eg, chloride), and/or high temperatures and pressures to ensure rapid leaching. However, most have proven too costly or too complex for industrial implementation, and none have achieved broad commercial success. Recently, a fresh approach to leaching primary copper concentrates has been developed at UBC, based on the use of inexpensive catalysts such as pyrite and activated carbon to accelerate the rate of chalcopyrite leaching under atmospheric conditions in mildly corrosive sulfate solutions, without fine grinding or chemical additives. These catalysts have also proven effective for the treatment of enargite, a highly refractory copper-arsenic sulfide mineral of increasing economic importance which is unsuitable for smelting. Most recently, we have discovered that pretreating pyrite samples with miniscule quantities of dissolved silver prior to leaching dramatically enhances their effectiveness as catalysts. The objective of the proposed research is to develop an understanding of the mechanisms underlying the catalytic effects of pyrite and activated carbon on primary copper sulfides, and to employ this understanding in the development of industrially robust leaching processes.